1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to an adjustable capacitor, a digitally controlled oscillator, and an all-digital phase locked loop, and more particularly, to an adjustable capacitor which connects a plurality of capacitor groups in a matrix form and selectively connects each capacitor group in parallel so as to adjust capacitance, and a digitally controlled oscillator and an all-digital phase locked loop using the same.
2. Description of the Related Art
Recently, high-definition television (HDTV) has been growing in popularity, and digital TV has been very much improved. However, since there are various digital TV standards, an analog TV standard has been still used widely. Accordingly, TV manufacturers request a design that could cover those various standards. However, it was not easy to have a TV tuner that can support various TV standards such as NTSC, PAL, ATSC and DVB using VHF/UHF/frequencies within the range of 40 MHz˜900 MHz.
In particular, it was difficult to embody a frequency synthesizer among TV tuner components that satisfies phase noise specifications within a wide frequency range. Accordingly, a sophisticated adjustable technology which can adjust to various frequency ranges was required.
A conventional analog PLL has a limited adjustable range, however the coefficient of all digital filters of an all-digital phase-locked loops (ADPLLs) circuit is programmable and thus the ADPLLs circuit is more appropriate and satisfies the above requirements better. In addition, if the ADPLLs circuit is used, the problem of low supply voltage and high leakage current occurring while an analog circuit is integrated may be overcome.
A digitally controlled oscillator (DCO) is a main component of ADPLLs and determines a frequency tuning range and phase noise performance of all systems. Conventionally, a plurality of oscillators are used to support broadband, but such embodiment causes product cost to increase and design efficiency to be reduced due to space restriction. Accordingly, a digitally controlled oscillator that supports broadband using a single LC circuit and satisfies phase noise specification is required.